User equipment and base station participating in a system information acquisition procedure

ABSTRACT

The present disclosure relates to a user equipment comprising a receiver receiving a minimum-system-information message from a first radio base station. System information for the first radio cell that can be acquired by the UE is UE Start carried within the minimum-SI message and one or more additional-SI messages. The minimum-SI message includes system information for accessing the first radio cell and at least one system information index, each of which is associated with one of the additional-SI messages. The SI message index comprises a value tag and an area pointer, the latter pointing to one area already defined. Processing circuitry determines whether the UE had already acquired before the additional-SI message associated with the same value tag and the same area. If the determination is positive, the processing circuitry determines that system information included in said additional-SI message acquired before is applicable to the first radio cell.

BACKGROUND Technical Field

The present disclosure is directed to methods, devices and articles incommunication systems, such as, 3GPP communication systems.

Description of the Related Art

Currently, the 3rd Generation Partnership Project (3GPP) works at thenext release (Release 15) of technical specifications for the nextgeneration cellular technology, which is also called fifth generation(5G). At the 3GPP Technical Specification Group (TSG) Radio Accessnetwork (RAN) meeting #71 (Gothenburg, March 2016), the first 5G studyitem, “Study on New Radio Access Technology” involving RAN1, RAN2, RAN3and RAN4 was approved and is expected to become the Release 15 work itemthat defines the first 5G standard. The aim of the study item is todevelop a “New Radio (NR)” access technology (RAT) which operates infrequency ranges up to 100 GHz and supports a broad range of use cases,as defined during the RAN requirements study (see, e.g., 3GPP TR 38.913“Study on Scenarios and Requirements for Next Generation AccessTechnologies”, current version 14.2.0 available at www.3gpp.org andincorporated herein its entirety by reference).

One objective is to provide a single technical framework addressing allusage scenarios, requirements and deployment scenarios defined in TR38.913, at least including enhanced mobile broadband (eMBB),ultra-reliable low-latency communications (URLLC), massive machine typecommunication (mMTC). A second objective is to achieve forwardcompatibility. Backward compatibility to Long Term Evolution (LTE,LTE-A) cellular systems is not required, which facilitates a completelynew system design and/or the introduction of novel features.

The fundamental physical layer signal waveform will be based on OFDM,with potential support of a non-orthogonal waveform and multiple access.For instance, additional functionality on top of OFDM such asDFT-S-OFDM, and/or variants of DFT-S-OFDM, and/or filtering/windowing isfurther considered. In LTE, CP-based OFDM and DFT-S-OFDM are used aswaveform for downlink and uplink transmission, respectively. One of thedesign targets in NR is to seek a common waveform as much as possiblefor downlink, uplink and sidelink.

Besides the waveform, some basic frame structure(s) and channel codingscheme(s) will be developed to achieve the above-mentioned objectives.The study shall also seek a common understanding on what is required interms of radio protocol structure and architecture to achieve theabove-mentioned objectives. Furthermore, the technical features whichare necessary to enable the new RAT to meet the above-mentionedobjectives shall be studied, including efficient multiplexing of trafficfor different services and use cases on the same contiguous block ofspectrum.

Since the standardization for the NR of 5^(th) Generation systems of3GPP is at the very beginning, there are several issues that remainunclear. For instance, there has been discussion on how to handle theprovision of system information by the network and the respectiveacquisition of the system information by the UEs. It is important toestablish and define effective processes to deliver system informationby the base stations and to acquire system information by the UEs.

BRIEF SUMMARY

One non-limiting and exemplary embodiment facilitates providing animproved system information procedure, in which different entities (UE,gNBs) are participating.

In one general aspect, the techniques disclosed here feature a userequipment. The user equipment comprises a receiver which receives aminimum-system-information message from a first radio base stationcontrolling a first radio cell of a mobile communication system. Systeminformation for the first radio cell that can be acquired by the userequipment is carried within the minimum-system-information message andone or more additional-system-information messages. Theminimum-system-information message includes system information foraccessing the first radio cell and includes at least one systeminformation index. Each system information index is associated with oneof the additional-system-information messages. The system informationmessage index comprises a value tag and an area pointer, wherein thearea pointer points to one area already defined. The user equipmentcomprises processing circuitry which determines whether the userequipment had already acquired before the additional-system-informationmessage being associated with the same value tag and the same area asindicated by the system information index received in theminimum-system-information message. If the determination is positive,the processing circuitry determines that system information included insaid additional-system-information message acquired before is applicableto the first radio cell.

In one general aspect, the techniques disclosed here feature a radiobase station. The radio base station comprises processing circuitrywhich generates a minimum-system-information message including systeminformation for accessing a first radio cell controlled by the radiobase station and including at least one system information index. Systeminformation for the first radio cell that can be acquired by the userequipment is carried within the minimum-system-information message andone or more additional-system-information messages. Each systeminformation index being associated with one of theadditional-system-information messages. The system information messageindex comprises a value tag and an area pointer. The area pointerpointing to one area already defined. The radio base station comprises atransmitter which transmits the minimum-system-information message tothe user equipment.

It should be noted that general or specific embodiments may beimplemented as a system, a method, an integrated circuit, a computerprogram, a storage medium, or any selective combination thereof.

Additional benefits and advantages of the disclosed embodiments will beapparent from the specification and Figures. The benefits and/oradvantages may be individually obtained by the various embodiments andfeatures of the specification and drawings, which need not all beprovided in order to obtain one or more of such benefits and/oradvantages.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

In the following exemplary embodiments are described in more detail withreference to the attached figures and drawings.

FIG. 1 shows an exemplary architecture for a 3GPP NR system,

FIG. 2 shows an exemplary user and control plane architecture for theLTE eNB, gNB, and UE,

FIG. 3 illustrates the user plane protocol stack for 5G NR,

FIG. 4 illustrates the control plane protocol stack for 5G NR,

FIG. 5 illustrates the messages exchanged between an eNB and a UE whenperforming a contention-based RACH procedure,

FIG. 6 illustrates the messages exchanged between an eNB and a UE whenperforming a contention-free RACH procedure,

FIG. 7 illustrates an exemplary signaling diagram for a X2 handoverprocedure of the LTE communication systems,

FIG. 8 illustrates three RAN-based notification areas, respectivelybeing composed of several gNBs, as well as a UE connected to gNB1 ofarea 1,

FIG. 9 illustrates the system information acquisition message exchangeas currently discussed for 5 g NR,

FIG. 10 illustrates the exemplary and simplified structure of a UE andan eNB,

FIG. 11 illustrates an exemplary scenario in which a UE, located at theradio cell of gNB1 is moving towards the radio cell 2 controlled bygNB2,

FIG. 12 shows the flow chart of an operation performed at the UE for theimproved system information acquisition procedure,

FIG. 13 illustrates the system information indexes for the correspondingadditional-SI messages, each being composed of an area pointer and avalue tag,

FIG. 14 illustrates the association between the area pointer and thearea type

FIG. 15 illustrates an exemplary implementation for the systeminformation indexes already illustrated in FIG. 13,

FIG. 16 illustrates an exemplary definition of different area types anddifferent system information validity areas for different additional-SImessages,

FIG. 17 illustrates the system information indexes for the correspondingadditional-SI messages, one of the system information indexes comprisingan area ID as well as a value tag while the other system informationindexes comprising area point and value text,

FIG. 18 illustrates the association between the area pointer and a listof area ID, and

FIG. 19 illustrates the system information indexes for the correspondingadditional-SI messages, each being composed of an area pointer and avalue tag.

DETAILED DESCRIPTION Basis of the Present Disclosure

5G NR System Architecture and Protocol Stacks

As presented in the background section, 3GPP is working at the nextrelease for the 5^(th) generation cellular technology, simply called 5G,including the development of a new radio access technology (NR)operating in frequencies ranging up to 100 GHz. 3GPP has to identify anddevelop the technology components needed for successfully standardizingthe NR system timely satisfying both the urgent market needs and themore long-term requirements. In order to achieve this, evolutions of theradio interface as well as radio network architecture are considered inthe study item “New Radio Access Technology”. Results and agreements arecollected in the Technical Report TR 38.804 v14.0.0, incorporated hereinin its entirety by reference.

Among other things, there has been a provisional agreement on theoverall system architecture. The NG-RAN (Next Generation-Radio AccessNetwork) consists of gNBs, providing the NG-Radio access user plane(SDAP/PDCP/RLC/MAC/PHY) and control plane (RRC) protocol terminationstowards the UE. The gNBs are interconnected with each other by means ofthe Xn interface. The gNBs are also connected by means of the NextGeneration (NG) interface to the NGC (Next Generation Core), morespecifically to the AMF (Access and Mobility Management Function) bymeans of the NG-C interface and to the UPF (User Plane Function) bymeans of the NG-U interface. The NG-RAN architecture is illustrated inFIG. 1, as taken from the TS 38.300 v.0.4.1, section 4 incorporatedherein by reference.

Various different deployment scenarios are currently being discussed forbeing supported, as reflected, e.g., in 3GPP TR 38.801 v14.0.0incorporated herein by reference in its entirety. For instance, anon-centralized deployment scenario (section 5.2 of TR 38.801; acentralized deployment is illustrated in section 5.4) is presentedtherein, where base stations supporting the 5G NR can be deployed. FIG.2 illustrates an exemplary non-centralized deployment scenario and isbased on FIG. 5.2.-1 of TR 38.301, while additionally illustrating anLTE eNB as well as a user equipment (UE) that is connected to both a gNBand an LTE eNB (which is to be understood as an eNB according toprevious 3GPP standard releases such as for LTE and LTE-A). As mentionedbefore, the new eNB for NR 5G may be exemplarily called gNB.

An eLTE eNB, as exemplarily defined in TR 38.801, is the evolution of aneNB that supports connectivity to the EPC (Evolved Packet Core) and theNGC (Next Generation Core).

The user plane protocol stack for NR is illustrated in FIG. 3, ascurrently defined in TS 38.300 v0.2.0, section 4.4.1. The PDCP, RLC andMAC sublayers are terminated in the gNB on the network side.Additionally, a new access stratum (AS) sublayer (SDAP, Service DataAdaptation Protocol) is introduced above PDCP as described in sub-clause6.5 of S TS 38.300 v0.2.0. The control plane protocol stack for NR isillustrated in FIG. 4, as defined in TS 38.300, section 4.4.2. Anoverview of the Layer 2 functions is given in sub-clause 6, of TS38.300. The functions of the PDCP, RLC and MAC sublayers are listed insub-clauses 6.4, 6.3, and 6.2 of TS 38.300. The functions of the RRClayer are listed in sub-clause 7 of TS 38.300. The mentioned sub-clausesof TS 38.300 v0.2.0 are incorporated herein by reference.

The new NR layers exemplarily assumed at present for the 5G systems maybe based on the user plane layer structure currently used in LTE(-A)communication systems. However, it should be noted that no finalagreements have been reached at present for all details of the NRlayers.

RRC States

In LTE, the RRC state machine consists of only two states, the RRC idlestate which is mainly characterized by high power savings, UE autonomousmobility and no established UE connectivity towards the core network,and the RRC connected state in which the UE can transmit user plane datawhile mobility is network-controlled to support lossless servicecontinuity.

The RRC in NR 5G as currently defined in section 5.5.2 of TR 38.804v14.0.0, incorporated herein by reference, supports the following threestates, RRC Idle, RRC Inactive, and RRC Connected, and allows thefollowing state transitions as defined in TR 38.804.

As apparent, a new RRC state, inactive, is defined for the new radiotechnology of 5G 3GPP, so as to provide benefits when supporting a widerrange of services such as the eMBB (enhanced Mobile Broadband), mMTC(massive Machine Type Communications) and URLLC (Ultra-Reliable andLow-Latency Communications) which have very different requirements interms of signaling, power saving, latency, etc.

RACH Procedure

No final agreement has been reached with regard to the RACH (RandomAccess Channel) procedure in 5G NR. As described in section 9.2 of TR38.804 v14.0.0, incorporated herein by reference, the NR RACH proceduremay support both contention-based and contention-free random access, inthe same or similar manner as defined for LTE. Also, the design of theNR RACH procedure shall support a flexible message 3 size, similar as inLTE.

The LTE RACH procedure will be described in the following in moredetail, with reference to FIGS. 5 and 6. A mobile terminal in LTE canonly be scheduled for uplink transmission, if its uplink transmission istime synchronized. Therefore, the Random Access Channel (RACH) procedureplays an important role as an interface between non-synchronized mobileterminals (UEs) and the orthogonal transmission of the uplink radioaccess. Essentially the Random Access in LTE is used to achieve uplinktime synchronization for a user equipment which either has not yetacquired, or has lost, its uplink synchronization. Once a user equipmenthas achieved uplink synchronization, the eNodeB can schedule uplinktransmission resources for it. One scenario relevant for random accessis where a user equipment in RRC CONNECTED state, handing over from itscurrent serving cell to a new target cell, performs the Random AccessProcedure in order to achieve uplink time-synchronization in the targetcell.

LTE offers two types of random access procedures allowing access to beeither contention based, i.e., implying an inherent risk of collision,or contention-free (non-contention based). A detailed description of therandom access procedure can be also found in 3GPP TS 36.321, section5.1. v14.1.0 incorporated herein by reference.

In the following the LTE contention based random access procedure isbeing described in more detail with respect to FIG. 5. This procedureconsists of four “steps”. First, the user equipment transmits a randomaccess preamble on the Physical Random Access Channel (PRACH) to theeNodeB (i.e., message 1 of the RACH procedure). After the eNodeB hasdetected a RACH preamble, it sends a Random Access Response (RAR)message (message 2 of the RACH procedure) on the PDSCH (PhysicalDownlink Shared Channel) addressed on the PDCCH with the (Random Access)RA-RNTI identifying the time-frequency slot in which the preamble wasdetected. If multiple user equipments transmitted the same RACH preamblein the same PRACH resource, which is also referred to as collision, theywould receive the same random access response message. The RAR messagemay convey the detected RACH preamble, a timing alignment command (TAcommand) for synchronization of subsequent uplink transmissions, aninitial uplink resource assignment (grant) for the transmission of thefirst scheduled transmission and an assignment of a Temporary Cell RadioNetwork Temporary Identifier (T-CRNTI). This T-CRNTI is used by eNodeBto address the mobile(s) which RACH preamble was detected until the RACHprocedure is finished, since the “real” identity of the mobile at thispoint is not yet known by the eNodeB.

The user equipment monitors the PDCCH for reception of the random accessresponse message within a given time window, which is configured by theeNodeB. In response to the RAR message received from the eNodeB, theuser equipment transmits the first scheduled uplink transmission on theradio resources assigned by the grant within the random access response.This scheduled uplink transmission conveys the actual random accessprocedure message like for example an RRC connection request or a bufferstatus report.

In case of a preamble collision having occurred in the first of the RACHprocedure, i.e., multiple user equipments have sent the same preamble onthe same PRACH resource, the colliding user equipments will receive thesame T-CRNTI within the random access response and will also collide inthe same uplink resources when transmitting their scheduled transmissionin the third step of the RACH procedure. In case the scheduledtransmission from one user equipment is successfully decoded by eNodeB,the contention remains unsolved for the other user equipment(s). Forresolution of this type of contention, the eNode B sends a contentionresolution message (a fourth message) addressed to the C-RNTI orTemporary C-RNTI.

FIG. 6 is illustrating the contention-free random access procedure of3GPP LTE, which is simplified in comparison to the contention-basedrandom access procedure. The eNodeB provides in a first step the userequipment with the preamble to use for random access so that there is norisk of collisions, i.e., multiple user equipments transmitting the samepreamble. Accordingly, the user equipment is subsequently sending thepreamble which was signaled by eNodeB in the uplink on a PRACH resource.Since the case that multiple UEs are sending the same preamble isavoided for a contention-free random access, essentially, acontention-free random access procedure is finished after havingsuccessfully received the random access response by the UE.

Thus, a similar or same RACH procedure as just explained in connectionwith FIGS. 5 and 6 could be adopted in the future for the new radiotechnology of 5G. However, 3GPP is also studying a two-step RACHprocedure for 5G NR, where a message 1, corresponding to message 4 inthe four-step RACH procedure, is transmitted at first. Then, the gNBwill respond with a message 2, corresponding to messages 2 and 4 of theLTE RACH procedure. Due to the reduced message exchange, the latency ofthe two-step procedure may be reduced compared to the four-stepprocedure. The radio resources for the messages are optionallyconfigured by the network.

LTE Handover Procedure

Mobility is a key procedure in LTE communication system. There are twotypes of handover procedures in LTE for UEs in active mode: theS1-handover and the X2-handover procedure. For intra-LTE mobility, thehandover via the X2 interface is normally used for the inter-eNodeBmobility. Thus, the X2 handover is triggered by default unless there isno X2 interface established or the source eNodeB is configured to useanother handover (e.g., the S1-handover) instead.

FIG. 7 gives a brief exemplary and simplified overview of the X2intra-LTE handover.

The X2 handover comprises a preparation phase (steps 4 to 6), anexecution phase (steps 7 to 9) and a completion phase (after step 9).The X2 intra-LTE handover is directly performed between two eNodeBs.Other entities of the core network (e.g., the MME, Mobility ManagementEntity) are informed only at the end of the handover procedure once thehandover is successful, in order to trigger a path switch to the neweNB.

More information on mobility procedures in LTE can be obtained, e.g.,from 3GPP TS 36.331 v14.2.2, section 5.4 incorporated herein byreference, and from 3GPP 36.423 v14.2.0 section 8.2 incorporated hereinby reference.

LTE-Closed Subscriber Group (CSG)

Closed Subscriber Group identifies a group of subscribers who arepermitted to access one or more CSG cells of the PLMN. The cell with CSGIndication set to be ‘TRUE’ is called ‘CSG Cell’. Non-CSG Cell (i.e., anOrdinary Cell) allows any UE to camp on as long as the UE has properPLMN info and the cell is not barred, but a CSG Cell allows only UEs tocamp on that belong to a specific CSG. A Closed Subscriber Groupidentifies subscribers of an operator who are permitted to access one ormore cells of the PLMN but which have restricted access (CSG cells).

To make a CSG call, UE should send CSG Id to which it belongs and itsaccess type in Attach request. MME then performs UE authentication withthe HSS and then exchanges Update Location Request and Answer. In UpdateLocation Answer, HSS sends CSG Information (CSG Id, Subscription timer)in Subscription data. MME then verifies the CSG Id with the CSG receivedin Attach request. If it matches, then UE proceeds the CSG call andsends Create session request with CSG Information IE to SGW. Uponreceiving of successful response from SGW, MME sends Attach Acceptmessage with Member status as ‘member’. After expiry of the Subscriptiontimer for which UE is subscribed to attach with CSG cell, MME initiatePDN connection deletion.

More detailed information on Closed Subscriber Groups can be foundthroughout 3GPP TS 36.304 v14.2.0 incorporated herein by reference.

Tracking Area

To reduce the overhead in the E-UTRAN and the processing in the UE, allUE-related information in the access network can be released during longperiods of data inactivity. The UE is then in the ECM-IDLE state (EPSConnection Management-IDLE). The MME retains the UE context and theinformation about the established bearers during these idle periods. Toallow the network to contact an ECM-IDLE UE, the UE updates the networkas to its new location whenever it moves out of its current TrackingArea (TA); this procedure is called a ‘Tracking Area Update’. Morespecifically, LTE introduced a mechanism of providing individualtracking area sizes for a UE by allowing the core network to provide alist of TAIs (Tracking Area Identities) that is considered the actualtracking area for this UE. When the UE leaves this combined area of thelist of TAs (e.g., the UE might receive a Tracking Area ID from a basestation, which is not in the list of TAs), the UE triggers a NAStracking area update (TAU) procedure. The same or a similar approachcould be foreseen for supporting mobility of a UE in RRC idle state inthe 5G NR. The core network area may be defined differently from theRAN-based notification area, which will presumably be as large orsmaller than the core network area.

The MME is responsible for keeping track of the user location while theUE is in ECM-IDLE. When there is a need to deliver downlink data to anECM-IDLE UE, the MME sends a paging message (core network initiatedpaging) to all the eNodeBs in the current TA of the UE, and the eNodeBsin turn send paging messages over the radio interface so as to reach theUE.

More detailed information on tracking areas can be found in 3GPP TS24.301 v14.3.0, incorporated herein by reference, e.g., in sections5.5.3, 8.2.26-8.2.29, 9.9.32, and 9.9.33

RRC States and RAN-Based Notification Areas

In LTE, the RRC state machine consists of only two states, the RRC idlestate which is mainly characterized by high power savings, UE autonomousmobility and no established UE connectivity towards the core network,and the RRC connected state in which the UE can transmit user plane datawhile mobility is network-controlled to support lossless servicecontinuity.

The RRC in NR 5G as currently defined in section 5.5.2 of TR 38.804v14.0.0, incorporated herein by reference, supports the following threestates, RRC Idle, RRC Inactive, and RRC Connected. As apparent, a newRRC state, inactive, is defined for the new radio technology of 5G 3GPP,so as to provide benefits when supporting a wider range of services suchas the eMBB (enhanced Mobile Broadband), mMTC (massive Machine TypeCommunications) and URLLC (Ultra-Reliable and Low-LatencyCommunications) which have very different requirements in terms ofsignaling, power saving, latency, etc. The new RRC inactive state shallthus be designed to allow minimizing signaling, power consumption andresources costs in the radio access network and core network while stillallowing, e.g., to start data transfer with low delay. The differentstates are characterized by sub-clause 5.5.2 of TR 38.804 v14.0.0incorporated herein by reference.

According to one characteristics of the new RRC inactive state, for theUE in RRC inactive the connection (both for user plane and controlplane) is maintained with RAN and the core network. In addition, thepaging mechanism (may also be called notification mechanism) for userequipments in that cell is based on so called radio access network,RAN-based notification areas (in short RNAs). The radio access networkshould be aware of the current RNA the user equipment is located in, andthe user equipment may assist the gNB to track the UE moving amongvarious RNAs.

A RNA can cover a single or multiple cells. It can be smaller than thecore network area, used for tracking a UE in RRC idle state. While theUE in RRC inactive state stays within the boundaries of the current RNA,it may not have to update its location with the RAN (e.g., gNB).Correspondingly however, when leaving its current RNA (e.g., and movingto another RNA), the UE may update its location with the RAN. There isnot yet a final agreement on how the RNAs are configured and defined.Sub-clause 5.5.2.1 of TR 38.804 v14.0.0, incorporated herein byreference, mentions several possible options that are currentlydiscussed.

FIG. 8 illustrates an example scenario where there are several RNAs,respectively composed of several gNBs. The UE is connected to a gNB1belonging to RNA1 and is assumed to move to gNB2 of RNA2. According toone option, a list of cells constituting the RAN-based notification areais defined. The UE is provided with an explicit list of cells (e.g., viadedicated signaling, i.e., signaling directly addressed to the UE, e.g.,an RRC connection reconfiguration message), such that the UE candetermine in which current RNA it is based on the current cell.According to another option, RAN areas are each being identified by aRNA ID. Each cell, specifically the gNB, broadcasts (at least one) RNAID (e.g., in its system information; alternatively or additionally, thisinformation can be transmitted to a UE using dedicated signaling) sothat a UE knows to which RAN area the cell belongs. At present, nodecision has been made as to whether to support one or both options, ormaybe a different solution is agreed upon in the future. Also no detailsare available about the RNA ID, such as its bit size, etc.

LTE System Information Acquisition

In LTE, system information is structured by means of system informationblocks (SIBs), each of which contains a set of functionally relatedparameters. The MIB (master information block) includes a limited numberof the most frequently transmitted parameters which are essential for aninitial access of the UE to the network. There are system informationblocks of different types SIB1-SIb18 currently defined in LTE to conveyfurther parameters, e.g., SIB1 includes parameters needed to determineif a cell is suitable for cell selection, as well as information aboutthe time domain scheduling of the other SIBs, SIB2 includes common andshared channel information.

Three types of RRC (Radio Resource Control) messages can be used totransfer the system information, the MIB, the SIB1 message and SImessages. SIBs other than SIB1 are transmitted within system informationmessages (SI messages), of which there are several, and which includesone or more SIBs which have the same scheduling requirements (e.g., thesame transmission periodicity). Depending on the content of the SImessages, the UE has to acquire different SI messages in idle andconnected states; e.g., 3^(rd). SI message, with SIB5 (inter-frequencycell reselection information) need to be acquired in idle state only.

The time-domain scheduling of the MIB and SIB1 messages is fixed withperiodicities of 40 ms and 80 ms respectively. The time-domainscheduling of the SI messages is dynamically flexible: each SI messageis transmitted in a defined periodically-occurring time-domain windowwhile the physical layer control signaling indicates in which subframeswithin the window the SI is actually being scheduled. The schedulingwindow of the different SI messages (in short SI window) are consecutiveand have a common length that is configurable. SI messages may havedifferent periodicities, such that in some clusters of SI windows (manyor) all of the SI messages are scheduled, while in other clusters onlythe SI messages with shorter repetition periods are transmitted. Systeminformation normally changes at specific radio frames and at a specificmodification period. LTE provides two mechanisms for indicating thatsystem information has changed. 1. Paging message including a flagindicating whether or not system information has changed, and 2. A valuetag in SIB1 which is incremented every time one or more of SI messageschange.

If the UE receives a notification of a change of SI, it starts acquiringthe system information from the start of the next modification period.Until the UE has successfully acquired the updated system information,it continues to use the existing parameters. If a critical parameterchanges, the communication may be seriously affected, but any serviceinterruption that may result is considered acceptable since it is shortand infrequent.

More information on the system information can be found in the 3GPPTechnical Specification TS 36.331 v14.1.0, section 5.2 “Systeminformation” incorporated herein in its entirety by reference.

NR System Information Acquisition

In 5G NR it is currently envisioned (although not finally agreed upon)that the system information is generally divided into a minimum systeminformation and other system information. The minimum system informationis periodically broadcast and comprises basic information required forinitial access to a cell (such as System Frame Number, SFN, list ofPLMN, Cell ID, cell camping parameters, RACH parameters). The minimumsystem information may further comprise information for acquiring anyother SI broadcast periodically or provisioned via on-demand basis,e.g., suitable scheduling information in said respect. The schedulinginformation may for instance include as necessary the SIB type, validityinformation, SI periodicity and SI-window information. Correspondingly,the other system information shall encompass everything that is notbroadcast in the minimum system information, e.g., cell-reselectionneighboring cell information.

The other SI may either be broadcast, or provisioned in a dedicatedmanner, either triggered by the network or upon request from the UE, asillustrated in FIG. 9. The other SI can be broadcast at a configurableperiodicity and for a certain duration. It is a network decision whetherthe other SI is broadcast or delivered through dedicated UE-specific RRCsignaling.

For the other SI that is actually required by the UE, before the UEsends the other SI request, the UE needs to show whether it is availablein the cell and whether it is broadcast or not. For the UE in RRCCONNECTED state, dedicated RRC signaling can be, e.g., used for therequest and delivery of the other SI.

In legacy LTE as briefly explained above, the UE is always required to(re-) acquire system information when cell change occurs and the UE isalso required to re-acquire all the system information when the systeminformation is changed (e.g., indicated by paging or an incremented,i.e., changed, value tag). For the new system in 5G NR, it is generallydesired to reduce the need to re-acquire system information byidentifying stored system information with a specific index/identifier,which is broadcast together with the minimum system information. It isassumed that some system information valid in one cell may be valid alsoin other cells. For example, the common radio resource configuration,the Access Class barring information, the UL carrier frequency andbandwidth, and the MB SFN (Multimedia Broadcast Single-FrequencyNetwork) subframe configuration may be valid among multiple adjacentcells.

More particularly, the specific index/identifier (which can beexemplarily called system information index) can be used to indicate thevalidity of associated system information in other cells. Thisindex/identifier can be applicable in more than one cell.

As a result, if the UE already stores valid system information, it isnot necessary to re-acquire that previously acquired and valid systeminformation. This allows reducing the UE power consumption and mayinvolve less signaling overhead on the air interface.

The system information index could be a single index or may be dividedinto two or more items, such as an area identifier and a value tag (sameor similar to LTE). The value tag, e.g., could be valid in one cell,while the complete system information index could then be consideredvalid in more than one cell as mentioned above so as to be able to avoidre-acquisition of system information.

There are no final agreements with regard to what the system informationindex is, or how it is signaled. Any signaling procedures to be definedfor 5G NR should at least provide configuration flexibility for thedefinition of the system information but should still keep the overheadof the transmission of system information at a minimum.

Another problem which may occur in the new 5G NR system is that for ahandover case, it may take a longer time (e.g., compared to LTE) for theUE to obtain all required SI messages from the target eNB, since somesystem information is not broadcast automatically by gNBs but is onlyavailable on demand after the UE sends out a corresponding other SIrequest (see above).

The present disclosure thus shall present solutions facilitating toovercome one or more of the disadvantages and/or meet one or more of therequirements mentioned above.

DETAILED DESCRIPTION OF PRESENT DISCLOSURE

In the following, UEs, base stations, and procedures will be describedfor the new radio access technology envisioned for the 5G mobilecommunication systems. Different implementations and variants will beexplained as well. The following detailed disclosure was facilitated bythe discussions and findings as described in the previous section “Basisof the present disclosure” and may be based at least on part thereof.

In general, it should be however noted that only few things have beenactually agreed on with regard to the 5G cellular communication systemsuch that many assumptions have to be made in the following so as to beable to explain the principles underlying the present disclosure in aclear and understandable manner. These assumptions are however to beunderstood as merely examples that should not limit the scope of thedisclosure. A skilled person will be aware that the principles of thefollowing disclosure and as laid out in the claims can be applied todifferent scenarios and in ways that are not explicitly describedherein.

Moreover, terms of the procedures, entities, layer layers, etc., used inthe following are closely related to LTE/LTE-A systems or to terminologyused in the current study items for 3GPP 5G, even though specificterminology to be used in the context of the new radio access technologyfor the next 3GPP 5G communication systems is not fully decided yet.Thus, terms could be changed in the normative phase, without affectingthe functioning of the embodiments of the disclosure. Consequently, askilled person is aware that the disclosure and its scope of protectionshould not be restricted to particular terms exemplary used herein forlack of newer or finally agreed terminology but should be more broadlyunderstood in terms of functions and concepts that underlie thefunctioning and principles of the present disclosure.

For instance, a mobile station or mobile node or user terminal or userequipment (UE) is a physical entity within a communication network. Onenode may have several functional entities. A functional entity refers toa software or hardware module that implements and/or offers apredetermined set of functions to other functional entities of a node orthe network. Nodes may have one or more interfaces that attach the nodeto a communication facility or medium over which nodes can communicate.Similarly, a network entity may have a logical interface attaching thefunctional entity to a communication facility or medium over which itmay communicate with other functional entities or correspondent nodes.

The term “base station” or “radio base station” here refers to aphysical entity within a communication network. The physical entityperforms some control tasks with respect to the communication device,including one or more of scheduling and configuration. It is noted thatthe base station functionality and the communication devicefunctionality may be also integrated within a single device. Forinstance, a mobile terminal may implement also functionality of a basestation for other terminals. The terminology used in LTE is e NB (oreNodeB), while the currently-used terminology for 5G NR is gNB.

The term “minimum-system-information message” refers to a particulartype of message carrying the minimum system information that is to bebroadcast in a radio cell for a UE accessing the radio cell. The“minimum-system-information message” is transmitted periodically in theradio cell, and its content can change. Other terminology used thereforis “minimum SI”. Functionally, the “minimum-system-information” issimilar to the MIB and/or the SIB1 used in legacy LTE systems.

Further system information for the radio cell can be transmitted using“additional-system-information messages”, which is a term referring toparticular types of messages carrying system information for the radiocell which is not broadcast within the minimum-system-informationmessage(s). Other terminology used therefor is “other SI”. Functionally,the “additional-system-information message” is similar to the SIBs usedin legacy LTE systems.

The term “system information index” refers to an information elementwhich is associated with the “additional-system-information message”,such that there is a one-to-one relationship between a systeminformation index and the associated “additional-system-informationmessage”. It should be noted however that it is not every“additional-system-information message” need be associated with a“system information index”. The system information index is to be usedin the context of the system information acquisition procedure todetermine the validity of the associated “additional-system-informationmessage”, as explained in the application, and shall allow the UE toavoid re-acquisition of system information in certain circumstances.

The term “area pointer” refers to an information element being part ofthe minimum-system-information message and specifically the systeminformation index. The area pointer shall not be understood as by itselfproviding any information on the area, but shall be understood to beacting as a pointer to additional information so as to allow determiningin combination an area (e.g., its type and/or ID). In specific examplesthe “area pointer” is functionally being used to encode the spatialvalidity of the additional-system-information message with which thesystem information index, in which it is included, is associated. Inother words, it is assumed that the system information within theadditional-SI message (additional-system-information message) is equallyapplicable (i.e., valid) in several radio cells, and that the validityin those several cells can be encoded into the “area pointer”, so as toallow UEs to determine the spatial validity of an additional-SI messagebased on the area pointer. The validity in time of an additional-SImessage is exemplarily encoded using the “value tag”.

The term “value tag” refers to an information element being part of theminimum-system-information message and specifically the systeminformation index. The value tag can be functionally used to encode thetemporal validity of the additional-system-information message withwhich the system information index, in which it is included, isassociated. In other words, it is assumed that the value tag is changed(e.g., incremented) every time the content of the additional-SI messageis changed, so as to allow UEs to determine the temporal validity of anadditional-SI message.

FIG. 10 illustrates a general, simplified and exemplary block diagram ofa user equipment (also termed communication device) and a schedulingdevice (here assumed to be located in the base station, e.g., the LTEeNB or the gNB in 5G NR). The UE and eNB/gNB are communicating with eachother over a (wireless) physical channel respectively using thetransceiver.

The communication device may comprise a transceiver and processingcircuitry. The transceiver in turn may comprise a receiver and atransmitter. The processing circuitry may be one or more pieces ofhardware such as one or more processors or any LSIs. Between thetransceiver and the processing circuitry there is an input/output point(or node) over which the processing circuitry, when in operation, cancontrol the transceiver, i.e., control the receiver and/or thetransmitter and exchange reception/transmission data. The transceivermay include the RF (radio frequency) front including one or moreantennas, amplifiers, RF modulator/demodulator and the like. Theprocessing circuitry may implement control tasks such a controlling thetransceiver to transmit user data and control data provided by theprocessing circuitry and/or receive user data and control data which isfurther processed by the processing circuitry. The processing circuitrymay also be responsible for performing processes of determining,deciding, calculating, measuring, etc. The transmitter may beresponsible for performing the process of transmitting. The receiver maybe responsible for performing the process of receiving.

A simple and exemplary scenario is assumed in the following. Asillustrated in FIG. 11 it is assumed that a UE is located in thecoverage are of radio cell 1 which is controlled by gNB1. One importantprocedure to be continuously performed by the UE is the systeminformation acquisition procedure. The system information acquisitionprocedure is, e.g., used to acquire the necessary system informationwhen powering up in the radio cell, when moving within the radio cell,and/or when moving to a new radio cell.

Based on the just discussed preliminary agreements and understandingreached in 3 GPP on the system information acquisition procedure for 5GNR, the provision of the overall system information is divided among aminimum-SI message and one or more additional-SI messages that are madeavailable to UEs in the respective radio cell(s). Although no agreementshave been reached yet, it is exemplarily assumed that there are fiveadditional-SI messages in total (e.g., termed SI1-SI5); any othersuitable number of additional-SI messages is equally possible.

The minimum-SI message is broadcast periodically by gNB1 to be acquiredfirst by the UE. The five additional-SI messages are either broadcastperiodically or are available for the UEs in the radio cell on demand(i.e., upon requesting the additional-SI message from gNB1); in eithercase, the UE is able to acquire the additional-SI messages and theembodiments are equally applicable. The minimum-SI message comprises theminimum system information that is to be broadcast in a radio cell for aUE accessing the radio cell and further comprises the necessaryscheduling information to enable the UE to obtain further systeminformation, i.e., by acquiring some or all of the additional-SImessages.

The different additional-SI messages include different types of systeminformation, some or all of which might not be strictly necessary forthe operation of the UE. Consequently, the UE may decide for eachadditional-SI message, whether its system information is even necessaryfor the operation of the UE in the radio cell. For instance, anadditional-SI message for the Earthquake and Tsunami Warning Serving(ETWS) notifications might not be considered necessary for the UE.According to an exemplary embodiment, the UE can exemplarily firstdetermine which of the additional-SI messages announced in theminimum-SI message are even necessary for its operation, beforecontinuing to determine whether acquisition of the requiredadditional-SI messages can be avoided as will be explained in detail inthe following. For ease of explanation of the different embodiments andvariants thereof, it is exemplary assumed that the UE considers all ofthe additional-SI messages (here, e.g., SI1-SI5) to be important for itsoperation and decides in principle to obtain all the correspondingsystem information therein. Whether the system information will indeedbe acquired by the UE, depends on the particular instance to avoidacquisition of same in certain circumstances as will be explained in thefollowing.

As explained before, there has been an agreement in 3GPP that the systeminformation acquisition procedure should be improved so as to avoidreacquisition of system information in certain circumstances.Correspondingly, the following embodiments described herein use a systeminformation index in connection with the additional-SI messages toencode the validity of the associated additional-SI message over timeand space (i.e., area), and thus to allow UEs to first determine thevalidity of the announced additional-SI message vis-à-vis previouslyacquired additional-SI messages and then to decide whether or notacquisition of that additional SI message is actually necessary.

At least one of the additional-SI messages can be associated with thesystem information index, in which case the minimum-SI message wouldcomprise at least for one of the five additional-SI messages (e.g., SI1)a system information index that is associated with that additional-SImessage (i.e., SI1). For the following explanations and in order toprovide the most benefit, in one exemplarily embodiment the concept ofusing a system information index to encode the validity of systeminformation is applied to all five additional-SI messages. Consequently,the minimum-SI message includes a system information index for each ofthe five existing additional-SI messages that can be acquired by the UEin radio cell 1.

Embodiments described herein pertain to a system information acquisitionprocedure performed between the UE and a gNB. The embodiments focus onimproving the way the validity of system information can be encoded anddecoded (respectively by a gNB and the UE) so as be able to avoid(re-)acquisition of system information (i.e., within the additional-SImessages) as well as to reduce overhead for the transmission of thesystem information and maintain flexibility in defining the validity ofsystem information over space (different areas/cells).

According to some exemplary embodiments, each of the system informationindexes is assumed to be composed of a value tag and an area pointerboth of which can be differentiated by the UE so as to be processedseparately from one another. The area pointer in the system informationindex, instead of directly including information on a specific area,rather “points” to an area that is already defined (the area may benetwork specific, but the user equipment should be aware of said area).The UE should be able to interpret the area pointer, i.e., to determinecorrectly to which area the area pointer in the system information indexis actually pointing. In said respect, the UE and the gNB should have acommon understanding on how to decode respectively encode an area intothe area pointer. The UE and gNB1, e.g., can store a list associatingpossible values of the area pointer with corresponding areas that arealready defined.

On the basis of the area pointer and the stored area list, the UE, uponreceiving the system information index including the area pointer, candetermine for which area the announced additional-SI message is deemedto be valid.

The value tag, as will be explained in more detailed embodiments later,can be used to determine the temporal validity of the announcedadditional-SI message.

The UE then needs to determine whether it is necessary to acquire any ofthe announced additional-SI messages from gNB1. In order to be able toavoid acquisition of any of the additional-SI messages that are acquiredbefore, the UE should have already received before the sameadditional-SI message with the same value tag and being associated withthe same area. In that case, the system information included in saidpreviously acquired additional-SI message can be considered to be stillapplicable to the present radio cell (within the same area), and thereis no need for the UE to again acquire the corresponding additional-SImessage comprising the same system information.

On the other hand, in case the value tag and/or the area (indicated bythe area pointer) of an additional-SI message as announced in the systeminformation index of the minimum-SI message are different from acorresponding value tag and/or a corresponding area associated with thecorresponding previously acquired additional-SI message, then the UEdetermines that the system information included in that previouslyacquired additional-SI message is not applicable in the radio cell.Thus, the UE determines that the UE needs to acquire the announcedadditional-SI message from the gNB so as to obtain valid systeminformation that is applicable to the present radio cell.

Consequently, since the area pointer merely points to an area instead ofproviding direct identification information for the area, the size ofthe area pointer can be smaller than a system information index directlyidentifying the area. Thus, less overhead is generated than compared toa system information index which directly includes an areaidentification.

The above described improved SI acquisition procedure also allows thegNB1 to flexibly determine the validity area of system information foreach additional-SI message separately, since a separate area pointer(which can be set differently from one another) is available in theminimum-SI message for each additional SI message.

FIG. 12 exemplarily illustrates a flow diagram for operating of a UE,particularly with regard to a basic system acquisition procedure asexplained above. The functioning of the above described improved SIacquisition procedure is described now in detail based on the followingexemplary two scenarios, described in connection with FIGS. 11 to 13. Ina first scenario it is exemplarily assumed that the UE is powering up inradio cell 1 of gNB1 and wants to access the radio cell 1 of gNB1 (thento be its serving gNB). gNB1 is broadcasting a minimum-SI messageperiodically, and the UE acquires same. The minimum-SI message includessystem information required for the UE for the initial access to theradio cell 1 and includes information on how to acquire additional-SImessages SI1-SI5 and the content thereof. Thus, among other things theminimum-SI message comprises for each additional-SI message acorresponding system information index, in turn including a particularvalue tag and area pointer. This is exemplarily illustrated in FIG. 13,which shows five system information indexes (SI_index_1-5) for the fiveavailable additional-SI messages SI1-SI5. For instance, SI_index_1,which is associated with additional-SI message SI1, comprises anarea_pointer_1 and value_tag_1; SI_index_2, which is associated withadditional-SI message SI2, comprises an area_pointer_2 and value_tag_2;and so on.

Considering that the UE is powering up for the first time, noadditional-SI messages have been acquired before at all and thus nosystem information is available with regard to the announcedadditional-SI messages. The UE thus determines for each additional-SImessage that it needs to acquire same in order to obtain thecorresponding system information contained therein. The UE can thusproceed to acquire the additional-SI messages SI1 up to SI5, asindicated in the minimum SI message; for instance, by receiving thoseadditional-SI messages broadcast by gNB1 at specific periodicallyoccurring radio resources and/or by first requesting and then receivingthose additional-SI messages that are only available in the radio cell 1on demand. Upon receiving the additional-SI messages, the UE may foreach additional-SI message store the area and value tag, derived fromthe system information index associated with the additional-SI message.For instance, for additional-SI message SI1, the UE will storevalue_tag_1 and information on the area pointed out by the area pointerarea_pointer_1 (e.g., the area ID and/or the type of the identifiedarea). The same or similar information can be stored by the UE for theother additional-SI messages SI2-SI5. The UE thus stores validityinformation for each additional-SI message, which can be used insubsequent system information acquisition procedures.

Now it is assumed that the UE keeps moving within the radio cell 1 andeventually moves to a different radio cell 2 controlled by gNB2 (seeFIG. 11). The UE will receive further minimum-SI messages within radiocell 1 and also upon entering the coverage area of radio cell 2. Theabove-described SI acquisition procedure can be repeatedly performed bythe UE, e.g., each time a minimum-SI message is received.

For instance, gNB2 broadcasts a minimum-SI message, which includessystem information required for a UE to make an initial access to radiocell 2 and further includes a system information index for each of theadditional-SI messages SI1-SI5. The structure of the system informationindex shall be the same as explained above for the minimum-SI messagebroadcast by gNB1 and thus is composed of a value tag and an areapointer. The UE then determines whether it is necessary to acquire anyof the announced additional-SI messages from gNB2. As explained before,the UE already acquired all of the additional-SI messages from gNB1,however has to determine whether these are also applicable in the newradio cell 2. This determination is performed by the UE based on thecontent of the system information index and the stored value tags andarea information. For each additional-SI message (e.g., SI1), the UEchecks the validity of the previously acquired additional-SI message(e.g., SI1) in radio cell 2 by comparing the value tag (e.g.,value_tag_1) stored for the previously-acquired additional-SI message(e.g., SI1) with the value tag (value_tag_1) included in the systeminformation index (SI_index_1) for the announced additional-SI message(SI1) in the newly received minimum-SI message. Furthermore, the UEchecks the validity of the previously acquired additional-SI message(e.g., SI1) in radio cell 2 by comparing the area stored for thepreviously-acquired additional-SI message (e.g., SI1) with the areapointed out by the area pointer (area_pointer_1) included in the systeminformation index (SI_index_1) for the announced additional-SI message(SI1) in the newly received minimum-SI message. If both the value tagand the area as announced in the new minimum-SI message are the same asthe value tag and the area stored for the previously acquiredadditional-SI message (e.g., SI1), the corresponding system informationincluded in that previously acquired additional-SI message (SI1) is alsoapplicable in radio cell 2 and the UE does not have to acquire theadditional-SI message via radio cell 2. This determination can beperformed for each additional-SI message. The sequence of checking thevalidity of the value tags and checking the validity of the areainformation is not restricted; i.e., the spatial validity can be checkedbefore the temporal validity, or vice versa, or in parallel.

Although the above scenario exemplarily assumed that the UE moved to anew radio cell 2, the improved system acquisition procedure can also beperformed by a UE staying within a cell. For instance, it can beexemplarily assumed that the spatial validity of system information willbe maintained as long as the UE stays in the same radio cell.Correspondingly, the area pointer broadcast in the system informationindex for the additional-SI messages will still point to the same areaas before. However, gNB1 might decide to change some system informationparameters in one or more of the additional-SI messages (e.g., in SI1).Accordingly, gNB1 will also change the value of the corresponding valuetag (e.g., value_tag_1, e.g., incrementing same by 1) and will broadcastthe changed value tag value in association with the changedadditional-SI message in the minimum-SI message. The UE, determiningthat the value tag value for an additional-SI message has changed,derives therefrom that the corresponding system information acquiredthrough the previous additional-SI message is no longer valid and willdetermine to re-acquire the corresponding additional SI message (e.g.,SI1) in radio cell 1 as transmitted by gNB1.

In the above, it has been assumed that the area pointer points to anarea already defined before. There may be various areas that can be usedin said respect. In general, it should be noted that typically one ormore areas are already defined with regard to other UE procedures. Forinstance, one or more tracking areas can be defined, so as to controlthe network-based mobility, as explained before. In addition, aRAN-based notification area can be defined, in order to implement thepaging mechanism when the UE is in the new RRC inactive state, asexplained before. Another example is a closed subscriber group areabeing composed of radio cells to which only particular UEs have access,as explained in more detail before.

Instead of using another area type to define the valid area of systeminformation (i.e., the area with a plurality of gNBs in which part ofthe system information is equally applicable), a new area type can bedefined for said purposes. Thus, a still further area that can be usedis a system information area, which is to be generally understood asbeing an area of a plurality of radio cells in which at least some ofthe system information is equally applicable. In other words, within onesystem information area, the radio cells use the same system informationparameters out of one or more additional-SI messages, and thus transmitthe same system information in its respective radio cell. No agreementsin 3GPP have been reached in said respect as to whether and, if so, howsystem information areas are defined, set up and maintained, etc.

The above explanation has focused on the procedures to be performedprimarily at the UE-side. However, the gNB also participates in theimproved system information acquisition procedure described above, byperforming the corresponding steps to provide the UE with the minimum-SImessage, the additional-SI messages. The gNB has to be able to generatethe content of the minimum-SI message particularly the systeminformation indexes to be associated with the additional-SI messages asdiscussed above and in the following.

Furthermore, since particular system information (of one or moreadditional-SI messages) shall be equally applicable in several radiocells of a specific area (such as a tracking area, or a CSG area, or aRAN-based notification area, or simply a system information area), thegNBs within these areas have to coordinate the system information of theadditional-SI messages as well as the system information indexes theybroadcast within the minimum-SI message. For example, if systeminformation of one additional-SI message is changed, all gNBs belongingto the validity area of that one additional-SI message have to besynchronized such that the same changed additional-SI message istransmitted and such that the same updated system information index(e.g., updated value tag) is broadcast in the minimum-SI message.

In the following an exemplary embodiment will be described according towhich the area pointer of the system information index encodes an areatype, based on which the UE is then in the position to determine thecorresponding area to which it points. It is exemplarily assumed thatthe area pointer is 2 bits long, thus being able to encode at most fourdifferent types of areas. An exemplary association between differentvalues of the area pointer and the corresponding area types isillustrated in FIG. 14 in form of an area type list with differentitems, where 00 encodes a tracking area type, 01 encodes a RAN-basedarea type, 10 encodes an SI area type, and 11 encodes a cell type. Itcan be assumed that the information of this association is stored by theUE, as well as in the gNB, so as to be able to encode and correctlydecode the area pointer information.

The system information index as illustrated in FIG. 13 is then composedof the value tag, which could be, e.g., 8 bits long, and the areapointer having 2 bits. Thus, each system information index is 10 bits,and the additional information carried by the minimum-SI message is 50bits (10 bits for each of the five additional-SI messages for which thesystem information index is included).

Correspondingly, the UE determines the area type based on the areapointer and the above mentioned area type association. Then, the UE maydetermine the actual area (e.g., the identification of the area) basedon the identified area type and by using identification informationpreviously acquired for the respective type of area. For instance,exemplarily assuming that the area pointer points to a tracking areatype (i.e., 00 in the example of FIG. 14), the UE is aware about the ID(or IDs) of the tracking area and may thus make the appropriateassociation between the tracking area type and the tracking areaidentification(s). The UE thus first determines that an announcedadditional-SI message is associated with a tracking area type so as tothen determine the current tracking area ID (as broadcast by gNB1).Then, following the improved system information acquisition procedure asexplained above, if that additional-SI message was already acquiredbefore and is valid for the same tracking area as the one announced inthe current minimum-SI message, there is no need for the UE to reacquirethat additional-SI message.

Put into different words, when the UE moves to a target cell whichbelongs to same tracking area as the source cell, the additional-SImessages that the UE acquired in the source cell are equally applicablein the target cell and re-acquisition of same can be avoided.

A similar approach is foreseen when the area pointer points to any ofthe other possible area types, e.g., the RAN-based notification area,the CSG area, or the system information area. In each case, the UEdetermines the area ID based on the area pointer, the above mentionedarea type association and finally the area ID for said identified areatype. The IDs of the RAN-based notification area, the CSG area and thesystem information area are known to the UE beforehand, e.g., broadcastby the gNB or provided to the UE in dedicated signaling.

Based on the thus determined area ID, the UE can determine whethersystem information previously-acquired in an additional-SI message isalso applicable in the current circumstances (e.g., in the new cell).Put briefly, if the target cell belongs to the same area (be itRAN-based notification area, CSG area, or system information area) asthe source cell, the additional-SI messages that the UE acquired in thesource cell are equally applicable in the target cell and re-acquisitionof same can be avoided.

In an exemplary scenario, the different types of areas will be explainedin connection with FIGS. 14, 15 and 16. As exemplarily assumed, the sameadditional-SI message SI1 (specifically the system information containedtherein) is applicable within one tracking area; the same additional-SImessage SI2 (specifically the system information contained therein) isapplicable within one RAN-based notification; the same additional-SImessage SI3 (specifically the system information contained therein) isapplicable within one system information area; and, the sameadditional-SI messages SI4/SI5 (specifically the system informationcontained therein) are applicable within one cell only. FIG. 15illustrates the values of the corresponding area pointers to reflect thedescribed scenario.

Correspondingly, for SI1, if the new cell and the old cell have the sameTracking Area ID (and also the same value in the value_tag_1), systeminformation contained in the additional-SI message SI1 acquired in theold cell can be used by the UE in the new cell as well. For SI2, if thenew cell and the old cell have the same RAN-based notification area ID(and also the same value in the value_tag_2), system informationcontained in the additional-SI message SI2 acquired in the old cell canbe used by the UE in the new cell as well. For SI3, if the new cell andthe old cell have the same system information area ID (and also the samevalue in the value_tag_3), system information contained in theadditional-SI message SI3 acquired in the old cell can be used by the UEin the new cell as well. On the other hand, the system information inadditional-SI messages SI4 and SI5 is cell specific (area pointer 11),and thus the UE has to acquire additional-SI messages SI4 and SI5 in anycase when entering the new cell.

According to a further exemplary embodiment, flexibility shall befurther increased on how the spatial validity is encoded into the systeminformation index of an additional-SI message. In the above embodiments,the valid area for system information is encoded into the area pointerfield of the system information index, allowing the UE to firstdetermine the area type and then the area ID. However, this solutionrequires that the UE is able to determine the area ID from simply thearea type, which could, e.g., require that the area ID is already knownto the UE beforehand (e.g., being broadcast in the radio cell). Thefollowing exemplary embodiment facilitates having the advantage that noprevious knowledge of an area ID is necessary, since the area ID isdirectly encoded into the system information index of an additional-SImessage.

FIG. 17 illustrates an exemplary configuration of the system informationindexes for the five additional-SI messages. As apparent therefrom, itis assumed that the system information index for additional-SI messageSI4 includes the area ID itself (e.g., a system information area IDhaving 8 bits) rather than an area pointer as the system informationindexes for the other additional-SI messages. The UE is correspondinglyable to determine the area ID from an area pointer as explained above,but is also able to process a system information index includingdirectly the area ID as illustrated in FIG. 17.

One exemplary way such that the UE knows whether a system informationindex includes an area pointer field (of, e.g., 2 bits) or an area ID(of, e.g., 8 bits) is the use of the ASN.1 coding. For the area pointerfield of each system information index, suitable ASN.1 coding allows todifferentiate and choose between the different fields, area pointerfield and area ID field. An exemplary ASN.1 coding can be as follows:

Area_Pointer CHOICE { area-pointer INTEGER (0 .. 3), -- 0: refer to theTracking Area type -- 1: refer to the RAN Area type -- 2: refer to theSI area type -- 3: cell type si-area-ID INTEGER (0 .. 255) }

In the following an exemplary embodiment will be described according towhich the area pointer of the system information index encodes an arealist item of an area list with area identifications. An exemplary listof area IDs is illustrated in FIG. 18, and the corresponding systeminformation indexes for the five additional-SI messages are illustratedin FIG. 19. As apparent therefrom, each system information index has thefield area pointer which value points to a list item of the area ID listof FIG. 18. It is exemplarily assumed that 3 bits are used for the arealist pointer field in the system information index, thus allowingdistinguishing up to 8 different area IDs (the actual area list size canbe dynamic, with a maximum of list items of 8). It is assumed that theUE has acquired the area ID list so as to be able to decode the areapointer of the system information index. One exemplary option is thatthat the area list is transmitted in the minimum-SI message as well, inwhich case the minimum-SI message carries both all system informationindexes as well as the area list. Another exemplary option is that thearea list is already obtained from a previous cell, e.g., during thehandover procedure as will be explained in more detail in laterembodiments.

Exemplary assuming 3 bits for the area list pointer and 8 bits for thevalue tag, 55 bits are necessary to transport the system informationindexes for all additional-SI messages. Additionally, the size of thearea list depends on its length (i.e., on the number of list items),where 8 bits per list item can be exemplarily assumed, i.e., 8 bits forthe ID; e.g., ASN.1 Code allows the UE to distinguish between thedifferent list items. Optionally, 3 bits can be foreseen in the arealist for the list item field.

This solution is particularly useful if only few different areas areused for the spatial validity of the system information. When multipleadditional-SI messages are associated with the same area (e.g., the sameSI area), one list item with the ID of that SI area suffices in thelist, such that the area list carried in the minimum-SI message does notget large. Also, in case a cell has multiple area IDs (e.g., trackingarea IDs or RAN-based notification area IDs), the discussed solutionallows the gNB to unambiguously identify the area ID.

According to further embodiments which can be used independently (e.g.,may be combined or used stand-alone) from the above discussedembodiments, the system information acquisition procedure in connectionwith the handover procedure should be improved. As explained before,some additional-SI messages are only available on demand, i.e., uponexplicit request of the UE at the gNB. When performing a handoverprocedure from a source cell to a target cell in line with the exemplaryhandover illustrated in FIG. 7, the UE reads the minimum-SI message ofthe target cell after the handover is completed, e.g., after step 9 ofFIG. 7. It is only then that the UE can determine which additional-SImessages should be acquired in the new target cell, e.g., following theimproved system information acquisition procedure explained above forone of the various embodiments. This is however time-consuming andinvolves many transactions between the entities.

According to these further embodiments, the handover procedure should beimproved in order to allow the UE to acquire the on-demand additional-SImessages earlier.

According to one of these embodiments, during the handover preparationphase the target gNB transmits the system information index broadcast bythe target gNB in its minimum-SI message to the source gNB, e.g., in theHandover Request ACK message (see step 6 of FIG. 7). The source gNB inturn can provide the target-cell-related system information indexes ofadditional-SI messages to the UE during the handover procedure, e.g., aspart of the handover command message. The UE, using thetarget-cell-related system information indexes, can determine which ofthe additional-SI messages available on demand in the target cell itwould like to acquire. Therefore, the UE already knows before thehandover is complete which additional-SI messages it would like toacquire, and can transmit the corresponding additional-SI messagerequest at an earlier point in time. For instance, the UE can transmitthe additional-SI message request during the handover execution phase,e.g., when performing the random access channel procedure with thetarget gNB (the RACH procedure between UE and target gNB can beperformed by the UE after receiving the handover command message fromthe source gNB. In said respect, one of the messages of the RACHprocedure can be used by the UE, e.g., using the Random Access Preambletransmission of the contention-free RACH procedure (see FIG. 6). Afurther subsequent message of the RACH procedure in the handoverscenario (not illustrated in FIG. 6; similar to the third message in thecontention-based RACH procedure) can carry the RRC ConnectionReconfiguration Complete message, termed in FIG. 7 Handover Completemessage.

The target-cell additional-SI message requested by the UE can bedelivered to the UE, e.g., in a message of the RACH Procedure (e.g., theRandom Access Respone message of the contention-free RACH procedure,subsequent to having received the additional-SI request in the firstmessage). Alternatively, the target gNB may use a different dedicatedmessage to provide the UE with the requested additional-SI message,subsequent to having received the additional-SI request in the RRCConnection Reconfiguration Complete message.

In an alternative embodiment, the UE itself is not required to requestthe on-demand additional-SI messages from the target cell, but this isdone by the source gNB during the handover preparation. In particular,the source gNB is informed by the UE on which additional-SI messages theUE would like to receive, e.g., through the measurement report message(see step 2 of FIG. 7). In turn, the source gNB requests theseadditional-SI messages from the target gNB, e.g., during the handoverpreparation procedure (e.g., in the Handover Request message, see step 4of FIG. 7). Similar to the previous alternative, the target gNB can thendeliver the target-cell additional-SI message requested by the UE to theUE, e.g., in a message of the RACH Procedure (e.g., the Random AccessResponse message of the contention-free RACH procedure). Alternatively,the target gNB may use a different dedicated message to provide the UEwith the requested additional-SI message.

Further Aspects

According to a first aspect, a user equipment is provided. The userequipment comprises a receiver which receives aminimum-system-information message from a first radio base stationcontrolling a first radio cell of a mobile communication system. Systeminformation for the first radio cell that can be acquired by the userequipment is carried within the minimum-system-information message andone or more additional-system-information messages. Theminimum-system-information message includes system information foraccessing the first radio cell and includes at least one systeminformation index. Each system information index is associated with oneof the additional-system-information messages. The system informationmessage index comprises a value tag and an area pointer, wherein thearea pointer points to one area already defined. The user equipmentcomprises processing circuitry which determines whether the userequipment had already acquired before the additional-system-informationmessage being associated with the same value tag and the same area asindicated by the system information index received in theminimum-system-information message. If the determination is positive,the processing circuitry determines that system information included insaid additional-system-information message acquired before is applicableto the first radio cell.

According to a second aspect provided in addition to the first aspect,if the determination is negative, the processing circuitry determinesthat system information included in said additional-system-informationmessage acquired before is not applicable to the first radio cell, anddetermines to acquire the additional-system-information message for thefirst radio cell from the first radio base station.

According to a third aspect which is provided in addition to the firstor second aspect, an area type list is stored in the user equipment,wherein each item in the area type list is associated with a list numberand an area type, wherein the area pointer indicates a list number ofthe area type list. The processing circuitry, when in operation,determines the area type based on the area pointer and the area typelist and determines an area identification based on the determined areatype and a previously acquired area identification for said determinedarea type. Optionally, the processing circuitry, when in operation,determines whether the additional-system-information message acquiredbefore is applicable for the same area based on the determined area typeand determined area identification.

According to a fourth aspect provided in addition to the third aspect,the area type is one of the following: a tracking area, a radio accessnetwork, RAN-based notification area, a closed subscriber group area, aradio cell, a system information area.

According to a fifth aspect provided in addition to the third or fourthaspect, the receiver, when in operation, receives a secondminimum-system-information message from the first radio base station ofthe first radio cell. The second minimum-system-information messageincludes system information for accessing the first radio cell andincludes one extended system information index. The extended systeminformation index is associated with one of theadditional-system-information messages. The extended system informationindex comprises a value tag and an identification of a systeminformation area. The processing circuitry, when in operation,determines whether the user equipment had already acquired before theadditional-system-information message being associated with the samevalue tag and the same system information area as included in theextended system information index. If said determination is positive,the processing circuitry, when in operation, determines that systeminformation included in said additional-system-information messageacquired before is applicable to the first radio cell.

According to a sixth aspect provided in addition to the first or secondaspect, the user equipment acquires an area list with corresponding areaidentifications. Each item in the area list is associated with a listnumber and an area identification, wherein the area pointer indicates alist number of the area list. The processing circuitry, when inoperation, determines the area identification based on the area pointerand the area list. Optionally, the user equipment acquires the area listfrom the received minimum-system-information message. Optionally, theprocessing circuitry, when in operation, determines whether theadditional-system-information message acquired before is applicable forthe same area based on the determined area identification.

According to a seventh aspect provided in addition to one of the firstto sixth aspects, the minimum-system-information message comprises onesystem information index per additional-system information-message thatcan be acquired by the user equipment in the first radio cell.

According to an eighth aspect provided in addition to any of the firstto seventh aspects, one or more of the additional-system-informationmessages can be broadcast by the first radio base station in the firstradio cell, or can be acquired by the user equipment upon requestingsame from the first radio base station.

According to a ninth aspect provided in addition to one of the first tothe eighth aspects, the processing circuitry, when in operation, storesthe received value tag of the system information index and informationon the area indicated by the system information index in associationwith the associated additional-system-information message. Optionally,the stored information on the area comprises information on the type ofthe indicated area and on the identification of the indicated area.

According to a tenth aspect provided in addition to one of the first toninth aspects, the receiver, when in operation, receives a secondminimum-system-information message from the first radio base station ofthe first radio cell. The second minimum-system-information messageincludes system information for accessing the first radio cell andincludes a second system information index. The second systeminformation index is associated with an additional-system-informationmessage that the user equipment has already acquired before. Theprocessing circuitry, when in operation, determines that content of thepreviously acquired system information message has changed whendetermining that the value of the value tag associated with thepreviously acquired additional-system-information message is differentfrom the value of a value tag included in the second system informationindex of the minimum-system-information message. The processingcircuitry, when in operation, determines to re-acquire theadditional-system-information message when determining that the contentof the previously acquired additional-system-information message haschanged.

According to an eleventh aspect provided in addition to one of the firstto tenth aspects, the system information message already acquired beforewas received by the receiver of the user equipment when the userequipment was located in a different radio cell or in the first radiocell.

According to a twelfth aspect provided in addition to any of the firstto eleventh aspects, the user equipment is moving to a second radio cellunder control of a second radio base station. The receiver, when inoperation, receives from the first radio base station at least onesystem information index associated with oneadditional-system-information message that the user equipment is able toacquire in the second radio cell upon requesting same. A transmitter ofthe UE, when in operation, transmits to the second radio base station arequest for acquiring the one additional-system-information messageindicated in the system information index that is associated with thesecond radio cell. Optionally, the request is transmitted by thetransmitter in a message of a random access channel procedure performedbetween the user equipment and the second radio base station when movingto the second radio base station. Optionally, the receiver, when inoperation, receives from the second radio base station the requestedadditional-system-information message in a message of the random accesschannel procedure, subsequent to the message used for transmitting therequest.

According to a thirteenth aspect provided in addition to any of thefirst to eleventh aspects, the user equipment is moving to a secondradio cell under control of a second radio base station. At least oneadditional-system-information message that the user equipment is able toacquire in the second radio cell is available upon requesting same. Thereceiver, when in operation, receives the additional-system-informationmessage from the second radio base station in a message of the randomaccess channel procedure.

According to a fourteenth aspect, a radio base station is provided. Theradio base station comprises processing circuitry which generates aminimum-system-information message including system information foraccessing a first radio cell controlled by the radio base station andincluding at least one system information index. System information forthe first radio cell that can be acquired by the user equipment iscarried within the minimum-system-information message and one or moreadditional-system-information messages. Each system information indexbeing associated with one of the additional-system-information messages.The system information message index comprises a value tag and an areapointer. The area pointer pointing to one area already defined. Theradio base station comprises a transmitter which transmits theminimum-system-information message to the user equipment.

According to a fifteenth aspect provided in addition to the fourteenthaspect, the transmitter, when in operation, transmits one or more of theadditional-system-information messages to the user equipment.Optionally, the processing circuitry, when in operation, determines thevalue of the area pointer of the system information index to indicate anarea in which the associated additional-system-information message isapplicable.

According to a sixteenth aspect provided in addition with the fourteenthor fifteenth aspect, the area pointer indicates a list number of an areatype list, wherein each item in the area type list is associated with alist number and an area type. The processing circuitry, when inoperation, determines the list number associated with the area type forwhich the additional-system-information message is applicable, and setsthe area pointer in the system information index for thatadditional-system-information message to indicate the determined listnumber. Optionally, wherein the area type is one of the following: atracking area, a radio access network, RAN-based notification area, aclosed subscriber group area, a radio cell, a system information area.

According to a seventeenth aspect provided in addition to any of thefourteenth to sixteenth aspects, the processing circuitry, when inoperation, generates a system information index to be associated withone additional-system-information message to include a value tag and anidentification of a system information area.

According to a eighteenth aspect provided in addition to the fourteenthor fifteenth aspect, the area pointer indicates a list number of thearea list, each item of the area list being associated with a listnumber and an area identification. The processing circuitry, when inoperation, determines the list number associated with the areaidentification for which the additional-system-information is applicableand sets the area pointer in the system information index for thatadditional-system-information message to indicate the determined listnumber. Optionally, wherein the processing circuitry, when in operation,generates the minimum-system-information message to include the arealist.

According to a nineteenth aspect provided in addition to any of thefourteenth to eighteenth aspects, the user equipment is moving to asecond radio cell under control of a second radio base station. Theradio base station comprises a receiver, which in operation, receivesfrom the second radio base station at least one system information indexassociated with one additional-system-information message that the userequipment is able to acquire in the second radio cell upon requestingsame. The transmitter, when in operation, transmits the received atleast one system information index relating to the second radio cell tothe user equipment. The receiver, when in operation, receives from theuser equipment a request for acquiring the oneadditional-system-information message indicated in the systeminformation index that is associated with the second radio cell.Optionally, the request is received by the receiver in a message of arandom access channel procedure performed between the user equipment andthe second radio base station when moving to the second radio basestation.

Hardware and Software Implementation of the Present Disclosure

The present disclosure can be realized by software, hardware, orsoftware in cooperation with hardware. Each functional block used in thedescription of each embodiment described above can be partly or entirelyrealized by an LSI such as an integrated circuit, and each processdescribed in the each embodiment may be controlled partly or entirely bythe same LSI or a combination of LSIs. The LSI may be individuallyformed as chips, or one chip may be formed so as to include a part orall of the functional blocks. The LSI may include a data input andoutput coupled thereto. The LSI here may be referred to as an IC(integrated circuit), a system LSI, a super LSI, or an ultra LSIdepending on a difference in the degree of integration. However, thetechnique of implementing an integrated circuit is not limited to theLSI and may be realized by using a dedicated circuit, a general-purposeprocessor, or a special-purpose processor. In addition, a FPGA (FieldProgrammable Gate Array) that can be programmed after the manufacture ofthe LSI or a reconfigurable processor in which the connections and thesettings of circuit cells disposed inside the LSI can be reconfiguredmay be used. The present disclosure can be realized as digitalprocessing or analogue processing. If future integrated circuittechnology replaces LSIs as a result of the advancement of semiconductortechnology or other derivative technology, the functional blocks couldbe integrated using the future integrated circuit technology.Biotechnology can also be applied.

Further, the various embodiments may also be implemented by means ofsoftware modules, which are executed by a processor or directly inhardware. Also a combination of software modules and a hardwareimplementation may be possible. The software modules may be stored onany kind of computer readable storage media, for example RAM, EPROM,EEPROM, flash memory, registers, hard disks, CD-ROM, DVD, etc. It shouldbe further noted that the individual features of the differentembodiments may individually or in arbitrary combination be subjectmatter to another embodiment.

It would be appreciated by a person skilled in the art that numerousvariations and/or modifications may be made to the present disclosure asshown in the specific embodiments. The present embodiments are,therefore, to be considered in all respects to be illustrative and notrestrictive.

The various embodiments described above can be combined to providefurther embodiments. All of the U.S. patents, U.S. patent applicationpublications, U.S. patent applications, foreign patents, foreign patentapplications and non-patent publications referred to in thisspecification and/or listed in the Application Data Sheet areincorporated herein by reference, in their entirety. Aspects of theembodiments can be modified, if necessary to employ concepts of thevarious patents, applications and publications to provide yet furtherembodiments.

These and other changes can be made to the embodiments in light of theabove-detailed description. In general, in the following claims, theterms used should not be construed to limit the claims to the specificembodiments disclosed in the specification and the claims, but should beconstrued to include all possible embodiments along with the full scopeof equivalents to which such claims are entitled. Accordingly, theclaims are not limited by the disclosure.

The invention claimed is:
 1. A user equipment, comprising: a receiver,which in operation, receives a minimum-system-information message from afirst radio base station controlling a first radio cell of a mobilecommunication system, wherein system information for the first radiocell that can be acquired by the user equipment is carried within theminimum-system-information message and one or moreadditional-system-information messages, the minimum-system-informationmessage including system information for accessing the first radio celland including at least one system information index, each systeminformation index being associated with one of theadditional-system-information messages, wherein the system informationmessage index comprises a value tag and an area pointer, the areapointer pointing to an area, processing circuitry, which in operation,determines whether the additional-system-information message stored inthe user equipment is associated with the same value tag and the samearea as indicated by the system information index received in theminimum-system-information message, and if the determination ispositive, the processing circuitry, when in operation, determines thatsystem information included in the stored additional-system-informationmessage is applicable to the first radio cell, wherein theminimum-system-information message comprises one system informationindex per additional-system information message.
 2. The user equipmentaccording to claim 1, wherein if the determination is negative, theprocessing circuitry, when in operation, determines that systeminformation included in the stored additional-system-information messageis not applicable to the first radio cell, and determines to acquire theadditional-system-information message for the first radio cell from thefirst radio base station.
 3. The user equipment according to claim 1,wherein an area type list is stored in the user equipment, wherein eachitem in the area type list is associated with a list number and an areatype, wherein the area pointer indicates a list number of the area typelist, wherein the processing circuitry, when in operation, determinesthe area type based on the area pointer and the area type list anddetermines an area identification based on the determined area type anda previously acquired area identification for the determined area type,and wherein the processing circuitry, when in operation, determineswhether the stored additional-system-information message is applicablefor the same area based on the determined area type and determined areaidentification.
 4. The user equipment according to claim 3, wherein thearea type is one of the following: a tracking area; a radio accessnetwork, RAN,-based notification area; a closed subscriber group area; aradio cell; and a system information area.
 5. The user equipmentaccording to claim 3, wherein the receiver, when in operation, receivesa second minimum-system-information message from the first radio basestation of the first radio cell, the second minimum-system-informationmessage including system information for accessing the first radio celland including one extended system information index, the extended systeminformation index being associated with one of theadditional-system-information messages, wherein the extended systeminformation index comprises a value tag and an identification of asystem information area, wherein the processing circuitry, when inoperation, determines whether the additional-system-information messagestored in the user equipment is associated with the same value tag andthe same system information area as included in the extended systeminformation index, and if the determination is positive, the processingcircuitry, when in operation, determines that system informationincluded in the stored additional-system-information message isapplicable to the first radio cell.
 6. The user equipment according toclaim 1, wherein the user equipment acquires an area list withcorresponding area identifications, wherein each item in the area listis associated with a list number and an area identification, wherein thearea pointer indicates a list number of the area list, wherein theprocessing circuitry, when in operation, determines the areaidentification based on the area pointer and the area list, wherein theuser equipment acquires the area list from the receivedminimum-system-information message, and wherein the processingcircuitry, when in operation, determines whether the storedadditional-system-information message is applicable for the same areabased on the determined area identification.
 7. The user equipmentaccording to claim 1, wherein one or more of theadditional-system-information messages can be broadcast by the firstradio base station in the first radio cell, or can be acquired by theuser equipment upon requesting same from the first radio base station.8. The user equipment according to claim 1 wherein the processingcircuitry, when in operation, stores the received value tag of thesystem information index and information on the area indicated by thesystem information index in association with the associatedadditional-system-information message, wherein the stored information onthe area comprises information on the type of the indicated area and onthe identification of the indicated area.
 9. The user equipmentaccording to claim 1, wherein the receiver, when in operation, receivesa second minimum-system-information message from the first radio basestation of the first radio cell, the second minimum-system-informationmessage including system information for accessing the first radio celland including a second system information index, the second systeminformation index being associated with an additional-system-informationmessage that is stored in the user equipment, wherein the processingcircuitry, when in operation, determines that content of the previouslyacquired system information message has changed when determining thatthe value of the value tag associated with the previously acquiredadditional-system-information message is different from the value of avalue tag included in the second system information index of theminimum-system-information message, and wherein the processingcircuitry, when in operation, determines to re-acquire theadditional-system-information message when determining that the contentof the previously acquired additional-system-information message haschanged.
 10. The user equipment according to claim 1, wherein the storedsystem information message was received by the receiver of the userequipment when the user equipment was located in a different radio cellor in the first radio cell.
 11. The user equipment according to claim 1,wherein the user equipment is moving to a second radio cell undercontrol of a second radio base station, wherein the receiver, when inoperation, receives from the first radio base station at least onesystem information index associated with oneadditional-system-information message that the user equipment is able toacquire in the second radio cell upon requesting same, wherein atransmitter, when in operation, transmits to the second radio basestation a request for acquiring the one additional-system-informationmessage indicated in the system information index that is associatedwith the second radio cell, wherein the request is transmitted by thetransmitter in a message of a random access channel procedure performedbetween the user equipment and the second radio base station when movingto the second radio base station, and wherein the receiver, when inoperation, receives from the second radio base station the requestedadditional-system-information message in a message of the random accesschannel procedure, subsequent to the message used for transmitting therequest.
 12. The user equipment according to claim 1, wherein the userequipment is moving to a second radio cell under control of a secondradio base station, wherein at least one additional-system-informationmessage that the user equipment is able to acquire in the second radiocell is available upon requesting same, wherein the receiver, when inoperation, receives the additional-system-information message from thesecond radio base station in a message of the random access channelprocedure.
 13. A radio base station, comprising: processing circuitry,which in operation, generates a minimum-system-information messageincluding system information for accessing a first radio cell controlledby the radio base station and including at least one system informationindex, wherein system information for the first radio cell that can beacquired by the user equipment is carried within theminimum-system-information message and one or moreadditional-system-information messages, each system information indexbeing associated with one of the additional-system-information messages,wherein the system information message index comprises a value tag andan area pointer, the area pointer pointing to an area, and atransmitter, which in operation, transmits theminimum-system-information message to the user equipment, wherein theminimum-system-information message comprises one system informationindex per additional-system information message.
 14. The radio basestation according to claim 13, wherein the transmitter, when inoperation, transmits one or more of the additional-system-informationmessages to the user equipment, wherein the processing circuitry, whenin operation, determines the value of the area pointer of the systeminformation index to indicate an area in which the associatedadditional-system-information message is applicable.
 15. The radio basestation according to claim 13, wherein the area pointer indicates a listnumber of an area type list, wherein each item in the area type list isassociated with a list number and an area type, wherein the processingcircuitry, when in operation, determines the list number associated withthe area type for which the additional-system-information message isapplicable, and sets the area pointer in the system information indexfor that additional-system-information message to indicate thedetermined list number, and wherein the area type is one of thefollowing: a tracking area, a radio access network, RAN,-basednotification area, a closed subscriber group area, a radio cell, asystem information area.
 16. The radio base station according to claim13, wherein the processing circuitry, when in operation, generates asystem information index to be associated with oneadditional-system-information message to include a value tag and anidentification of a system information area.
 17. The radio base stationaccording to claim 13, wherein the area pointer indicates a list numberof the area list, each item of the area list being associated with alist number and an area identification, wherein the processingcircuitry, when in operation, determines the list number associated withthe area identification for which the additional-system-information isapplicable and sets the area pointer in the system information index forthat additional-system-information message to indicate the determinedlist number, and wherein the processing circuitry, when in operation,generates the minimum-system-information message to include the arealist.
 18. The radio base station according to claim 13, wherein the userequipment is moving to a second radio cell under control of a secondradio base station, wherein the radio base station comprises a receiver,which in operation, receives from the second radio base station at leastone system information index associated with oneadditional-system-information message that the user equipment is able toacquire in the second radio cell upon requesting same, wherein thetransmitter, when in operation, transmits the received at least onesystem information index relating to the second radio cell to the userequipment, wherein the receiver, when in operation, receives from theuser equipment a request for acquiring the oneadditional-system-information message indicated in the systeminformation index that is associated with the second radio cell, andwherein the request is received by the receiver in a message of a randomaccess channel procedure performed between the user equipment and thesecond radio base station when moving to the second radio base station.